Siwa is Bayek's home in Assassin's Creed Origins. Bayek is a Medjay from the Siwa Oasis in Egypt, and the game begins there before expanding across a large recreation of Ptolemaic Egypt. His connection to Siwa is central to his identity as a protector and local authority.
The opening story shows Bayek returning to Siwa after an absence and becoming entangled in a conspiracy involving masked figures. His investigation eventually leads to the formation of the Hidden Ones, the organization that becomes the Assassin Brotherhood. The desert oasis setting also distinguishes Bayek's early missions from the game's later urban environments.
Alexandria is an important city in Origins, especially through Bayek's relationship with Aya and the game's political storyline. Memphis and Cyrene are also visited locations. None of them is Bayek's home; that distinction belongs to Siwa Oasis.